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| Oscilloscope for CD eye pattern |
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| abhi1981:
I'm planning to buy an oscilloscope. Will the Siglent SDS1052DL(50Mhz, 500MSa/s) oscilloscope be able to display a CD eye pattern, like an analog oscilloscope? Or do I need 1GSa/s? Please advise. |
| tooki:
500MSa/sec is more than enough for that. |
| wasedadoc:
An audio CD carries 2 channels of 16 bits at 44,100 samples per second. That is a net data rate of less than 1.5 Mbyte/s. There is extensive error correction which means the gross rate read from the CD is significantly higher but nowhere near the rate that would trouble even a 50 MHz bandwidth scope to show the eye pattern. |
| tooki:
It’s eight-to-fourteen modulation, so 44100s-1x 2ch x 16bits x (14/8) = 2.4696Mbps. But yeah, there’s a screenshot elsewhere on the forums of a CD eye diagram on a digital scope, and it was running at just 100MSa/sec. |
| paschulke2:
The raw data rate of a compact disc is approx. 4.3Mbit/s (audio data + data for error correction + subcode + ...). With the help of the eight to forteen modulation this datarate falls in a frequency band of 20kHz to 1.5MHz on the disc (Heemskerk and Shouhamer Immink (1982) Compact Disc: system aspects and modulation, Philips tech. Rev. 40, 157-164). Therefore neither sample rate nor bandwidth of any half-decent scope will be a problem. But: In case of a digital scope you need a scope with a high number of waveforms per second and good intensity grading . Typically an eye pattern is done at 500ns/div (5µs for the complete screen). For a good eye pattern you should have more than 5000 waveforms per second. A bad digital scope - even with high bandwidth and sample rate - will be worse than almost any old 20MHz analog scope. |
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